Thank you guys :)

I created the room with walls first and despite trying to be very carefull, as I ran into trouble with double walls before, somehow I messed it up.

I just re-created the room from scratch, this time room first, walls later, then adding the slopes and it worked like a charm.

I ...

Hi,

I uploaded an example: http://ul.to/u6attfyz

The ceiling should be visible in bright purple but instead one can see the sky. What am I doing wrong?

Regards
Simon